(1) Field of the Invention
The present invention relates to recovery of high-temperature inflammable exhaust gases from the partial combustion of fuel and air in a combustor apparatus.
(2) Description of the Prior Art
Various combustor apparatus capable of generating high-temperature inflammable exhaust gases containing less non-combustible products, such as ash, suitable to burn a boiler, have been developed. Such gases are recovered from the partial combustion of a mixture of fuel and oxidizer air in a combustor apparatus, which may be designed as the first reaction zone of a boiler system to supply fuel to the second reaction zone. In the first reaction zone, the fuel mixture is burned at or above the slag fusion temperature, generally at atmospheric pressure or near atmospheric pressure, to produce combustible exhaust gases which are recovered and burned in the second reaction zone to produce steam.
Combustor apparatus for partial fuel combustion comprises a cylindrical combustion chamber and a tangential injection duct through which fuel mixtures, which may be pulverized coal carried with air, are injected into the combustion chamber. The fuel introduced through the tangential passage of the injection duct, upon entering the combustion chamber, develops into a rapidly swirling vortex. This rapid movement causes most of the ash and other non-combustible products present in the fuel mixture to move externally as molten slag, forming the outermost part of the swirling gaseous stream, and can be expelled from a slagging port mounted at the outside wall of the combustion apparatus. The central portion of the rapidly swirling vortex is recovered from the outlet port of the combustion chamber as high-temperature exhaust gases. The exhaust gases thus obtained contain substantial quantities of incompletely combusted by-products such as carbon monoxide and hydrogen, and are passed to the associated boiler or recycled for other applications.
However, the boiler would have poor burning on an air-fuel equivalence ratio of lower than 0.6. In conventional exhaust gas recovery method from the partial combustion of coal and air, combustion apparatus have been burned on mixtures of fuel and air as oxidizing gas with an air-fuel equivalence ratio in the range from 0.6 to 0.7. The resultant exhaust gases, recovered following partial combustion in the reaction chamber of the apparatus, have tended to turn out somewhat lacking in inflammability. These recovered gases, which may be used after cooling, have failed to provide efficient thermal energy when burned in a boiler. Experiments showed that the partial combustion at 0.7 air-fuel equivalence ratio produced waste gases of heating value ranging nor more than 200-500 kcal/Nm.sup.3, depending on the kinds of coal making up the fuel mixtures.
Furthermore, conventional waste gas recovery methods have been proved to pose problems with coal gasification. Generally, requirements for gasification differ from one application to another in which the gases recovered are intended for. For high thermal energy, the gases must have an increased methane content, which means combustion under a pressure of over 20 kg/cm.sup.2 G. Facilities capable of operation at high reaction pressure levels add much to production costs.